Device on a platform

ABSTRACT

There is disclosed a device on a platform, especially a semi submersible platform ( 10 ), comprising a number of pontoons ( 16 ), and a platform deck ( 12 ), which is connected to the topside surface of the pontoons by way of a number of columns ( 18, 20 ) or legs. The device is characterized in that in connection to the topside surface ( 34 ) of each pontoon ( 16 ), upward extending wall sections ( 26 ) are formed so that an upward open chamber ( 28 ) is defined.

[0001] The present invention relates to a device as described in the introduction of the subsequent claim 1.

[0002] More precisely, the invention concerns a device on a semi submersible platform (a so-called semi-sub) that can improve its properties both for transit and during its use in partly submerged state.

[0003] Semi submersible platforms are used for many purposes offshore, and especially for carrying out drilling for, and production of, hydrocarbons offshore. They can also be used for other purposes.

[0004] Semi submersible platforms consist of two or more extended pontoons. From the topside or each pontoon, a number, i.e. as a rule two or three, columns or legs extend upwards. Mounted on top of these legs is a deck with equipment for carrying out operations such as drilling and production. Furthermore, the platform is arranged so that it can be moved over long distances by its own power. This is done by each pontoon being comprised of an approximate bow construction that decides the direction of travel, and internally, in each pontoon, is propulsion machinery which drives the propeller so that the platform can be moved.

[0005] During the operation of the platform, the platform is lowered downwards into the sea such that the pontoons will lie completely below the surface of the water. The deck is positioned so high up that any oncoming waves only hit the platform columns. When the platform shall be moved, it is again raised so that the pontoons are lying only partially under water, and with the aid of the propulsion machinery/propellers the platform can be moved to another user area. If the sea is getting heavy, it will still hit the topside of the pontoons. In many ways, this can impede the progress of the platform. And, furthermore, when the platform is in a submerged state, it would be desirable to improve its movement properties.

[0006] With the invention, one aims for a solution which leads to improved travelling properties during propulsion in the sea when the platform shall be moved, at the same time as good properties during operation are maintained or are improved.

[0007] In particular, this will be significant in movements such as rolling, stamping and heaving. It is necessary that the response of the semi-sub to waves is as good as possible, especially in exposed regions, because many operations which are to be carried out are critical, for example, when drilling through reservoirs with high pressure.

[0008] Improved movement properties of a semi-sub are achieved by, for one thing, the introduction of square corners on columns and pontoons. Thereby, one achieves an additional mass effect which reduces the response of the semisub to incoming waves.

[0009] However, this shape is not favourable for the propulsion properties of the semisubs and reduces the speed considerably.

[0010] With known embodiments of semisubs, their propulsion properties have been given little weight because semisubs normally lie in one place for a long time, for example, at drilling after oil and gas.

[0011] Semisubs, which have been anchored, use tug-boats for moving. Other semisubs are moved by their own propulsion installation. Nevertheless, this type of rig takes a long time to move, and the operations are costly.

[0012] Drilling after oil and gas occurs in steadily deeper waters and in areas in which the fields lie far away from each other. At the same time, it has become very usual that sub-sea production wells lie spread out over large areas on the sea bottom.

[0013] In addition, drilling technology has made considerable advances and wells today are drilled both faster and more efficiently. The time elapsed is often reduced to under half when compared to earlier. Therefore, floating drilling installation must spend relatively more of their time in moving between wells that are to be drilled.

[0014] With the present invention, one aims to improve the propulsion properties of a semi-sub, with the movement properties during operations being maintained or being improved.

[0015] The device according to the invention is intended to give positive additional properties during stationary operations, especially during heaving-, pitching- and rolling movements. During user the inventive construction will function both as a bilge keel, which reduces the rolling, at the same time as the additional mass effects give a reduction of the stamping- and heaving movements.

[0016] In raised position (de-ballasted), the walls of the construction behave as the sides of the hull of a catamaran. The rest of the construction can thereby be shaped with soft, rounded forms to get the best possible propulsion properties. Thereby, during travel the water will flow easily along the sides of the hull and will cause little resistance.

[0017] Furthermore, it is an aim of the invention to provide a solution that results in the platform becoming even more steady when it is partly submerged.

[0018] The device according to the invention is distinguished by the features which are evident in the characteristics in the subsequent claim 1.

[0019] Further features of the device invented are described in the dependent claims 2-8.

[0020] The device according to the invention shall be explained further in the subsequent description with reference to the enclosed figures, in which:

[0021]FIG. 1 shows a side view of a semi submersible platform (semisub) where the invention is applied.

[0022]FIG. 2 shows a perspective view of one of the pontoons of the platform, including the invented solution.

[0023]FIGS. 3A and 3B show in plane view and side view, respectively, an alternative embodiment of the invention.

[0024] Identical parts of the drawn details are given the same reference number in the different figures. Initially, reference is made to FIG. 1 in which the semi submersible platform 10 is shown in side view. The platform comprises a deck with the necessary equipment, such as a derrick 14. Furthermore, the platform is comprised of a number of pontoons 16 (two or more). The deck 12 is connected to the pontoons by way of columns 18, 20. The usual construction is, as shown in the figure, that the platform is comprised of two parallel pontoons, each of which is connected to the deck 12 by two columns. The invention can be used on all types of platforms with pontoons, for example, platforms with three pontoons running in parallel, see claim 8.

[0025] When a platform such as this shall be moved from one field to another, it is raised up so that, on the whole, only the pontoon is sticking down into the water. The platform moves by operating the propellers 22, 24 underneath the pontoons. To decrease the resistance during such transport, each pontoon 16 is formed, especially at its end sections, with a hull-construction which has an approximate bow-shape similar to the underwater part of a ship.

[0026] With the present invention, in connection with each pontoon 16, an upwardly extending wall construction 26 with a suitable height, is formed, and which forms an upward facing open chamber 28. When the platform is submerged, this chamber is filled with, water and will then contribute to the increase of the pontoon mass which must be moved/pushed when the platform moves in the waves. When the platform is raised for transfer, the chamber 28 is emptied of water, such as by pumping with its own pump system, or by draining naturally through openings in the wall and includes hatches which can be opened (such as by remote control from the control centre of the platform) for free drainage of water. Optionally slots 40 (see FIG. 3b), which are permanently open, can be fitted. Preferably, the slots are made in the lower part of the wall 26 where it joins the wall- or floor parts of the pontoon, i.e at the bottom of the chamber 28. It is a considerable advantage that the upward extending wall joins the pontoon sides and column sides with even/smooth and rounded lines/surfaces as shown in FIG. 3B. Another alternative is that the slots comprise through-running channels which connect the bottom part of the chamber 28 with the sea environment outside the pontoon. Furthermore, such channels can be comprised of valves that can close for inward/outward flow of water, which is particularly practical when the platform is moving/travelling. Here, there are many possibilities for solutions. The upward extending wall parts 26 will then function as ship's sides on a hull. The side walls 26 extend preferably so high (H see FIG. 2) above the topside surface (34) of the pontoon (16), that the waves which hit against the pontoon 16 will normally not go over the top of the wall 26 and enter the chamber 28. The two ends of the wall construction, i.e. up to what is a bow/stern section of the pontoon, are formed with such smooth rounding off that the resistance to flow during travel is as small as possible.

[0027] According to a preferred embodiment, as is shows in FIG. 2, the wall part in the vertical- or height direction is aligned with the side surfaces of the pontoon itself.

[0028] According to an alternative and especially preferred embodiment, the arch-shaped side surfaces to the columns 18, 20, are used as wall-forming bodies. This means that the upward extending extra wall part only runs between the columns to form the inner chamber. This embodiment is shown schematically in FIG. 3A in plane section.

[0029] It will be evident that the whole (as in FIG. 2) or parts (as in FIG. 3) of the topside surface 34 of the pontoons form a floor or bottom in the mentioned chamber 28.

[0030] In addition to these two alternatives which are shown in FIGS. 2 and 3, the construction invented can be formed in many different embodiments. For example, when a platform is comprised of three pontoons running in parallel, the two outer pontoons can comprise the chamber-forming construction invented, while the middle pontoon is without such a chamber-forming construction. 

1. Device on a platform, especially semi submersible platform (10), comprising a number of pontoons (16), and a platform deck (12) which are connected to the topside surface of the pontoons by way of a number of columns (18, 20) or legs, characterised in that in relation to the topside surfaces (34) of mainly all the pontoons (16), upward extending wall sections (26) are formed so that an upward facing open chamber (28) is defined.
 2. Device in accordance with claim 1 , characterised in that the wall sections are aligned with the wall parts of the pontoon.
 3. Device in accordance with claims 1-2, characterised in that the wall sections (26) are combined with the upward extending side surfaces of the columns (16, 18), so that these make up a part of the upward extending wall sections which define the upward open chamber (28).
 4. Device in accordance with claims 1-3, characterised in that the whole or parts of the topside surfaces (34) of the pontoons form a floor in the mentioned chamber (28).
 5. Device in accordance with claims 1-4, characterised in that each wall section have a height H above the topside surface (34) of the pontoon (16).
 6. Device in accordance with claims 1-5, characterised in that the chamber (28) is adapted to be emptied of water by pumping out with its own pipe/pumping system.
 7. Device in accordance with claims 1-6, characterised in that the wall part (26) is comprised of channels/openings/slots (40) with, if desired, closable hatches/valves which can be opened (such as by remote control from the control centre of the platform) for free outflow and inflow of water.
 8. Device in accordance with one of the preceding claims, characterised in that the platform is comprised of three pontoons running essentially in parallel, and the two outer pontoons comprise the chamber-forming construction invented, while the middle pontoon is without such a chamber-forming construction. 